Common Lisp

Common Lisp (CL) is a dialect of the Lisp programming language, published in American National Standards Institute (ANSI) standard document ANSI INCITS 226-1994 (S2018) (formerly X3.226-1994 (R1999)). The Common Lisp HyperSpec, a hyperlinkedHTML version, has been derived from the ANSI Common Lisp standard.

The Common Lisp language was developed as a standardized and improved successor of Maclisp. By the early 1980s, several groups were already at work on diverse successors to MacLisp: Lisp Machine Lisp (aka ZetaLisp), Spice Lisp, NIL and S-1 Lisp. Common Lisp sought to unify, standardize, and extend the features of these MacLisp dialects. Common Lisp is not an implementation, but rather a language specification. Several implementations of the Common Lisp standard are available, including free and open-source software and proprietary software products. Common Lisp is a general-purpose, multi-paradigm programming language. It supports a combination of procedural, functional, and object-oriented programming paradigms. As a dynamic programming language, it facilitates evolutionary and incremental software development, with iterative compiling into efficient runtime programs. This incremental development is often done interactively without interrupting the running application.

It also supports optional type annotation and casting, which can be added as needed at the later profiling and optimization stages, to permit the compiler to generate more efficient code. For instance, fixnum can hold an unboxed integer in a range supported by the hardware and implementation, permitting more efficient arithmetic than on big integers or arbitrary precision types. Similarly, the compiler can be told on a per-module or per-function basis which type of safety level is wanted, using optimize declarations.

Common Lisp includes the Common Lisp Object System (CLOS), an object system that supports multiple dispatch (multimethods) and method combinations. It is often implemented with a metaobject protocol.

Common Lisp is extensible through standard features such as Lisp macros (code transformations) and reader macros (input parsers for characters).

Common Lisp provides partial backwards compatibility with Maclisp and John McCarthy's original Lisp. This allows older Lisp software to be ported to Common Lisp.